Basically, the whole premise of the show is that the whole world become unconscious at the exact same time. For approximately 2 minutes, everyone experiences what they call a "flash" foreward. Most of them believe it was a 2 or so minute picture of the future.

As the show has continued, some of the things that they saw in the flash starts occuring. For example, one man sees his daughter on the battle field. Strange for him because he knew his daughter as being dead for years. One day, she shows up in his house, quite a live.

There's a lot to explain, but basically, that's the premise of the show.